My mom is letting me dye my hair in a salon for my birthday but she said that she wont pay for touch ups every 6 months so i was thinking to just get semi perminate hair dye but how long dose it last?

Semi permanent color gradually fades with each shampoo. The color will last longer depending how often you shampoo. Go with a demi permanent. It will last longer than the semi and will fade out naturally. The coverage is better too.